I realize my questions are very basic, that is because my background is a bit different, and I have to understand these terms to be able to do my work I guess all people here are famiilar with these basic things, please help me, I would appreciate your time ....... what we mean if we say need to take wave functions as a Gaussian processes??????what is Ensemble average???Stochastic prosses????? due to the dispersion relation in quantum mechanics the eigenvalues are degenerate, how this is related to each other???????what we mean by clean system, and dirty state???????